Photomechanical printing



Dec. 5, 1933. R. E. HURsT ET AL 1,938,291

PHOTOMECHANICAL PRINTING (NEGATIVE COLLOID RELIEF) Filed May 16, 1932 Fl Z Me In [In ne mgoaseJ emulszbn .5 was/Led am' P87720 Ve WAJl//AL Mh.25. Haifa-Z 67201205* E', Mezlemtye atto/pump.

Patented Dec. 5, 1933 UNITED STATES PHOTOlVIECHANICAL PRINTING (NEGATIVECOLLOID RELIEF) Ralph Emerson Hurst and Charles Edmund Meulendyke,Rochester, N. Y. v

Application May 16, 1932. Serial No. 611,646

16 Claims.

This invention relates especially to the preparation of metallic sheetssupporting a colloid layer containing a sensitive silver salt with orwithout an actinic-light restraining agent and 3 to the subsequentprocessing of such sheets into relief, planographic and intaglio platesfor monochrome and polychrome printing.

Within the scope of these improvements and Within the art ofphoto-mechanical printing We 11) intend to include new and usefulmaterials and the processing of the same into relief printing plates asfor line and half-tone engraving, intaglio printing plates as forphotogravure and rotogravure, and planographic printing plates as forphoto-metallography and offset printing.

Generally speaking in the preparation of al photomechanical printingplate it is necessary to coat a metallic sheet with a colloid layercontaining a light-sensitive salt. In the present state of the art thislayer generally consists of a bichromated glue or other colloid. Uponexposure under a photographic negative the glue becomes insoluble Wherethe light penetrates.

Upon washing in water the unaieoted glue disf solves out leaving apositive colloid relief. This colloid relief can then serve as a resistso that the metal can be etched where unprotected by the resist. Themetallic plate so etched when properly inked can serve as a printingplate.

C ri'here are objections to a bichromated colloid appreciated by thoseskilled in the art. A bichromated colloid layer rapidly deterioratesrequiring preparation shortlyvbefore using. It has too littlesensitivity for direct exposure in the camera and even requires severalminutes exposure to day light in contact printing. The essentiallyhand-preparation of metallic plates so sensitized is labor-consuming andtime-consuming. A ready-prepared plate of good keeping quality wouldtend to be cheaper, of better and more uniform printing quality and ofgreater freedom from defects, derived from the ordinary advantages ofquantity-production. Also plates capable of direct exposure in thecamera would tend to simplify existing processes. In its favor it may besaid that a bichromated colloid can yield an image of high quality andhigh resolution as evidenced by clean separation of half-tone dots.

It is the purpose of this invention to prepare a metallic sheetsupporting a light-sensitive colloid layer of good keeping quality, ofsuilcient sensitivity for direct exposure in the camera and capable ofbeing directly transformed into a printing plate which in quality cancompare most favorably with that aiorded. by a Wet co1- lodion negativeprinted onto a sheet sensitized with bichromated glue. In referring to ametallic sheet we intend to include metal in the form of a sheet, plate,cylinder, foil, deposition or other form. We Will now describe in ageneral Way the steps by which such improvements are accomplished. Laterwe will show the practicality of such improvements as carried out in atypical branch of the photo-mechanical printing industry.

It is a fact that what is known as a photographic emulsion can be coatedon a glass plate and that such coated plate can be made with goodkeeping quality and with sufcient sensitivity 'for direct exposure inthe camera. A process gelatin dry plate is an example. A photographicemulsion consists of a sensitive silver salt incorporated in a colloidmedium which is generally gelatin. In referring to a sensitive salt Weintend to include those silver salts capable of exposure and developmentwhich are ordinarily coated on photographic plates, films and papers,and in referring to colloid we intend to in- 0 clude not only gelatinbut other equivalent co1- loids.

It is also a fact that a developed silver image in a gelatin layer canbe treated with a bichromate in solution to render .the gelatininsoluble under the selective-control of the silver image, that is tosay, the gelatin surrounding the developed silver particles becomesinsoluble. Thus a photographic image can be converted into a colloidprint of differentially hardened gelatin. If the soluble gelatin isdissolved out a colloid relief is left analogous to that which can beobtained withA a layer of bichromated glue which has been exposed andthe unaffected glue dissolved out in water. Itv is apparent that by thisprocess direct exposure in the camera will produce a negative colloidrelief. In our companion application iiled May 7, 1932, Serial No.609,997 We propose to use the same materials but process them so that ondirect exposure in the camera they yield directly an image which is apositive colloid relief. There are other methods of producing directly anegative colloid relief including the tanning developer but We preferthe bichromate method. L,

The general method which We propose is to coat lo a metallic sheet witha photographic emulsion of sulicient sensitivity for contact printing orfor direct exposure in the camera, to expose and develop the silverimage, to render the gelatin insoluble by a suitable agent under theselective control of the silver image, to dissolve out the solublegelatin thus forming a colloid resist' directly supported by the metaland to subsequently convert to a printing plate by appropriate means.The accomplishment of making and processing metallic sheets directlycoated with emulsion presented diiiculties to be overcome. Aphotographic emulsion coated directly upon the ordinary materials ofprinting plates such as zinc and copper gave rapid deterioration of theemulsion. The well-known types of sensitizing generally employed inphoto-mechanical work such as bichromated glue and sensitive bitumen canbe coated directly on metallic surfaces without danger of metalliccontamination. The particular type of sensitizing which we propose hasdecided advantages in speed and color sensitivity but its direct coatingupon metal has hitherto been associated with metallic contamination. Toavoid this it has been proposed to protect such sensitizing byinterposing a layer of lacquer or varnish between the sensitizing andthe metallic surface and also to treat the metallic surface so as toform a protecting layer of metallic oxides or salts. The first methodgreatly increases the number of steps and the difficulties ofprocessing. The second method furnishes a very doubtful means ofprotection and a troublesome layer in processing. We have beensuccessful in plating a basic metallic sheet with a metallic layer whichis truly inert to a directly supported emulsion layer. An example is acopper base sheet which is plated with silver, nickel, or chromium, andsubsequently coated with emulsion. We have thus produced a metallicsheet which can be directly coated with emulsion without thecontamination hitherto associated with directly coated metal. Thismetallic protecting layer is integral with the metallic base sheet anddoes not interfere with any subsequent etching of the metal. It has allthe advantages of a protecting layer without the disadvantages of theabovementioned layer of lacquer or varnish. The surface of suchprotecting metallic layer is preferably slightly grained to promote theadhesion of the sensitizing layer. A well-grained surface is preferablein preparing planographic printing plates by this method. The use of asubbing to promote the adhesion of the sensitizing layer to the metallicsurface is preferably to be avoided, but we intend any use of suchsubbing to be ineluded within the meaning of a metallic surface directlysupporting a sensitizing layer. The method of electro-plating ispreferably used in the formation of the protecting metallic layer. it isessential that the electro-plated layer shall be of adequate thicknessand free from excessive porosity or intercrystalline fracture. t isnecessary to guard against metallic and non-metallic contaminationswhich might be present in the plating-bath and carried down asocclusions or intercrystalline films. Chromium and nickel are preferablyused instead of silver. They are cheaper, do not tarnish readily, andafford a harder surface more resistant to wear and abrasion and to thecorrosive action of certain metallic inks.

At this point we will describe a manner in which a suitable source ofemulsion can be obtained. An emulsion such as is suitable for a processdry plate is suitable for performing the operations herein described.There are Various formulas published for making emulsions fortransparencies and process plates, but a more convenient source is toremove the emulsion from a readyprepared plate. However most commercialplates are hardened, that is to say, the gelatin has been renderedinsoluble by an agent such as chrome alum, so that the emulsion cannotbe readily removed from the plate and readily dissolved. We secured froma manufacturer process plates coated without a hardening agent. Bysoaking one of these plates in cold water until the emulsion absorbedabout ten times its weight in water, then scraping off the emulsion Witha knife or straight edge and dissolving at a temperature around 100Fahrenheit, a convenient source of emulsion was available. Inasmuch asthe processing depends upon formation of insolubilized gelatin it ispreferable to use an unhardened emulsion.

Up to this point we have described the preparation of metallic sheetswhich have b'een plated with metal as a means of protecting the emulsionfrom deterioration. Also we have described a simple way of securing asource of prepared emulsion.

A convenient 'method of coating a metallic plate is to take a definiteamount of the melted emulsion and pour upon the slightly warmed plate,tilting the plate in different directions until the emulsion has evenedout, then placing upon a chilled marble slab to set the emulsion, afterwhich the plate can be dried'in a gentle current of air. Another way isto pour on an excess of emulsion and to drain off in the fashion ofpreparing a wet collodion plate. It is obvious that these operationsmust be carried on in a photographic dark room.

Assuming that we have coated a metallic plate with an emulsion asdescribed above an exacting and typical method of employing theimprovements embodied in this invention is to expose the sheet tosuitable copy in the camera behind a half-tone screen. A 60 line screenand a 133 screen afford a practical range. With a coating thickness ofemulsion approximating that of a normal dry plate, and treating thenormally exposed and developed plate with bichromate solution to obtaindots of insolubilized gelatin, we found that upon treatment with warmwater the Whole colloid layer was removed from the support. It wasevident that if the insolubilized gelatin dots were to adhere to thesupport that the exposure of both high-lights and shadows must strikethrough suciently so that upon processing there will be no solublegelatin under the insolubilized dots. On the other hand on coating theemulsion too thinly, the high-lights tended to be over-exposed beforethe shadows were properly rendered, giving halation and poor resolutionof dots. We found that excellent results could be obtained when thethickness of the emulsion layer and the exposure were properlycorrelated. Further we found that the expedient of adding alight-restraining agent to the emulsion aided the control of theexposing and processing operations. An example of such agent is theyellow dye tartrazin which can be added in the proportion of a trace to.2 gram of dye to 10 grams of the melted emulsion described above.However either with or Without addition of the dye we obtained theconditions whereby upon exposure in the camera and processing theinsolubilized gelatin dots in both high-lights and shadows were 'welldefined and remained attached to the support, and whereby the spacesbetween such dots were clean bare metal. In the case of contact printingsuch as exposing under a half-tone negative somewhat differentconditions obtain than for direct exposure through a half-tone screen inthe camera. Due to excessive spreading of the image upon exposure incontact printing we found the use of a light-restraining agent necessaryfor satisfactory results.

An emulsion such as used above which has not been made color-sensitiveis largely sensitive to blue and violet light and a dye such astartrazin which does not harm the emulsion can be added to it. Theyellow color acts as a lter to hold back the penetrationV of the blueand violet light to which the emulsion is sensitive. The presence of theiight-restraining agent prevents halation, holds back the high lightexposure to the benefit of the shadows, localizes the developed silverfor easier formation of insolubilized gelatin, and gives a print andcolloid relief of sharp denition. In the case of an emulsion which hasbeen made sensitive to some other color such as green or red it would ofcourse be necessary to employ dyes which would absorb the green or thered to get an equivalent light-restraining action. For example with redsensitive emulsion, napthol green would tend to absorb red radiation.

There has been previous use of a light-restraining agent in an emulsionlayer coated upon a transparent support, notably motion picture film,and a developed relief obtained after exposing through the back of thesupport. In that case thickness of the emulsion layer is of littleimportance and having been exposed through the baci; oi the support, thedeveloped relief naturally adheres to it. There is also no danger ofmetallic contamination to the emulsion. We believe that we are the rstto propose coating a colloid layer containing a sensitive silver saltwith or without an actinic-light restraining agent directly upon ametallic sheet consisting of a base sheet plated with a metallic layertruly inert to the emulsion.

We believe that we are the iirst to prepare and move all traces ofsulrltes which might later react th the bichrornate to forminsolubilized gelatin. shed sheet with or without drying is then abichrornate bath. A convenient bath sts of 8 grams ci potassiumbichrornate and oi potassium bromide dissolved in l liter rater. thisbath the gelatin corresponding ne developed silver image becomesinsoluble while remaining gelatin retains its original solublecondition. The reaction is complete in about two minutes. lt isunnecessary to fix out the residual silver salts or to bleach out thedevelc cped silver. 'By treatment with hot water the soluble gelatin isremoved so that we have a metallic sheet supporting a colloid relief.Where bare metal is exposed between the insolubilized gelatin dots themetal can be etched by some suitable agent. Ferrie chloride can. be usedto etch the protecting layer of nickel, dilute hydrochloric acid :toretching chromium, and dilute nitric acid for etching silver.

.as a specific example oi the application of the new and useiulimprovements embodied in this invention, let us taire the case ofphotogravure. Normally, in the present state of the art the followingsteps are required:

l. Making of the negative.

2. Making of a laterally reversed positive.

3. Sensitizing of a transfer tissue with bichromate.

4. Exposing the tissue through the positive and through a screen.

5. Transferring the colloid print to metal.

6. Developing (in warm water) the colloid relief.

There is involved in the above a long series of steps. There are three.photographic images. There are the diicult and time-consuming steps ofpreparing the sensitized tissue and making the transfer. There are thelong exposures of the tissue. By employing a ready-prepared metallicplate supporting a colloid layer containing a sensitive silver salt, asdescribed in this specification, we can expoe the same directly in thecamera and behind a gravure screen and directly obtain a negative incorrect lateral position. Upon treating the developed image withbichromate the photographic image becomes the colloid image. There isone photographic image instead of three, no hand preparation ofmaterials, no long exposures, and no transfer.

-lt will thus be seen that we have described materials and processeswith all necessary details, i

embodying the principles and attaining the objects and advantages of theinvention. Since many matters of treatment, manipulation, selection andproportion of ingredients, succession of steps and other details may bevariously modied without departing from the principles involved, we donot intend any limitation to such details 'excepting so far as set forthin the appended claims.

For the purpose of illustrating the several steps which can be followedin carrying out the method herein described and at the same timedisclosing the article in its several stages of development, attentionis called to the accompanying drawing in which:

Figure l shows a greatly enlarged section of a metallic base sheet l,plated with a layer of inert metal 2, directly supporting a silverhalide emulsion layer 3.

Figure 2 shows the emulsion layer as exposed under a half-tone screenand developed, exposed areas l being subsequently hardened.

Figure '3 shows the emulsion layer the un= exposed soluble areasdissolved out at 5.

Figure Ll shows the plate etched through the inert metallic layer intothe base plate corresponding to areas 6 unprotected by the emulsionresist.

Figure shows the completed plate with the emulsion resist removed.

What is claimed is:

l. A material for 'use in the art of photomechanical printing includinga basic metallic sheet whose surface is plated with a metallic layertruly inert to and directly supporting a colloid layer containing asensitive silver salt.

2. A material for use in the art of photomechanical printing including abasic metallic sheet whose surface is plated with a metallic silverlayer directly supporting a colloid layer containing a sensitive silversalt.

3. A. material for use in the art of photomechanical printing includinga basic metallic sheet whose suriace is plated with a metallic nickellayer directly supporting a colloid layer chromium layer directlysupporting a colloid layer containing a sensitive silver salt.

5. A material for use in the art of photomechanical printing including abasic metallic sheet Whose surface is plated with a metallic layer trulyinert to and directly supporting a colloid layer containing a silversalt made sensitive to specic radiation by a suitable sensitizing dye.

6. A material for use in the art of photomechanical printing including abasic metallic sheet whose surface is plated with a metallic layer trulyinert to and directly supporting a colloid layer-containing a sensitivesilver salt and an actinic-light restraining agent.

7. A material for use in the art of photomechanical printing including abasic metallic sheet Whose surface is plated with a metallic layer trulyinert to anddirectly supporting a colloid layer containing a silver saltmade sensitive to specific radiation by a suitable sensitizing dye andcontaining anV actinic-light restraining agent of a color non-actinic tothe sensitized silver salt.

8. In the art of photo-mechanical printing, the method of producing ametallic sheet supporting a photographic colloid relief including thesteps of exposing a basic metallic sheet Whose surface is plated With ametallic layer truly inert to and directly supporting a colloid layercontaining a sensitive silver salt, developing the silver image,rendering the colloid insoluble by a suitable agent under the selectivecontrol of the silver image, and dissolving out the soluble colloid.

9. In the art of photo-mechanical printing, the method of producing ametallic sheet supporting a photographic colloid relief including thesteps of exposing a basic metallic sheet Whose surface is plated with ametallic layer truly inert to and directly supporting a colloid layercontaining a sensitive silver salt, developing the silver image,rendering the colloid insoluble by a suitable agent under the selectivecontrol of theA silver image, said agent containing a bichromate, anddissolving out the soluble colloid.

l0. In the art of photo-mechanical printing, the method of producing ametallic sheet supporting a photographic colloid print including thesteps of exposing a basic metallic sheet Whose surface is plated with ametallic layer truly inert to and directly supporting a colloid layercontaining a sensitive silver salt, developing the silver image andrendering the colloid insoluble by a suitable agent under the selectivecontrol of the silver image.

l1. In the art of photo-mechanical printing, the method of producing ametallic sheet supporting a photographic colloid relief including thesteps of exposing a basic metallic sheet whose surface is plated with ametallic layer truly inert to and directly supportinga colloid layercontaining a sensitive silver salt and an actiniclight restrainingagent, developing the silver image, rendering the colloid insoluble by asuitable agent under the` selective control of the" silver image, anddissolving out the soluble colloid.

12. In the art of photo-mechanical printing, the method of producing ametallic sheet supporting a photographic colloid print including thesteps of exposing a basic metallic sheet whose surface is plated with ametallic layer truly inert to and directly supporting a colloid layercontaining a sensitive silver salt and an actinic-light restrainingagent, developing the silver image, and rendering the colloid insolubleby a. suitable agent under the selective control of the silver image.

' 13. In the art of photo-mechanical printing, the method of producing aprinting plate including the steps of exposing a basic metallic sheetWhose surface is plated with a metallic layer truly inert to anddirectly supporting a colloid layer containing a sensitive silver salt,developing the silver image, rendering the colloid insoluble by asuitable' agent under the selective control of the silver image,dissolving out the soluble colloid, and etching the metallic surface bya suitable agent under the selective control of the colloid image.

14. In the art of photo-mechanical printing, the method of producing aprinting plate including the steps of exposing a basic metallic sheetWhose surface is 'plated with a metallic layer truly inert to anddirectly supporting a colloid layer containing a sensitive silver salt,developing the silver image, rendering the colloid insoluble by asuitable agent un der the selective control of the silver image, andetching the metallic surface by a suitable agent under the selectivecontrol of the colloid image.

l5. In the art of photo-mechanical printing, the method of producing aprinting plate including the steps of exposing a basic metallic sheetWhose surface is plated with a metallic layer truly inert to anddirectly supporting a colloid layer containing a sensitive silver saltand an actinic-light restraining agent, developing the silver image,rendering the colloid insoluble by a suitable agent under the selectivecontrol of the silver image, dissolving out the soluble colloid, andetching the metallic surface by a suitable agent under theselective'control of the colloid image.

16. In the art of photo-mechanical printing, 125 the method of producinga printing plate including the steps of exposing a basic metallic sheetwhose surface is plated with a metallic layer truly inert to andsupporting a colloid layer containing a sensitive silver salt and anactinic-light 130 restraining agent, developing the silver image,rendering the colloid insoluble by a suitable agent under the selectivecontrol of the silver image, and etching the metallic surface by asuitable agent under the selective control of the colloid 135 image.

RALPH EMERSON HURST. CHARLES EDMUND

